Factors Influencing Migratory Behavior of Burrowing Owls in Southern ArizonaEPA Grant Number: FP916396
Title: Factors Influencing Migratory Behavior of Burrowing Owls in Southern Arizona
Investigators: Ogonowski, Mark S.
Institution: University of Arizona
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $70,082
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Fellowship - Zoology , Academic Fellowships , Biology/Life Sciences
The objectives of this research project are to determine the migratory status of a partially migratory population of owls and to test hypotheses regarding the causes of overwintering for those animals who do not migrate, including the role of food abundance. Given the recent and rapid changes in migratory status observed for populations of many bird species, the results of this study may contribute both to the conservation of burrowing owls and to a better understanding of the plasticity of avian migratory behavior. The western subspecies of the burrowing owl Athene cunicularia hypugaea is found in undisturbed grassland and desert areas and various human-altered landscapes across the western United States and southwestern Canada. Recent population declines and apparent range contraction across many areas of its distribution have led to concerns over the status of this unique ground-dwelling raptor. Declines have been attributed to loss of breeding habitat, reductions in populations of fossorial mammals, and the effects of habitat change on wintering grounds. The species’ migratory patterns and wintering ecology remain poorly understood, and the proportion of migrant animals within burrowing owl populations appears to vary by region.
The project will take place in the Tucson metropolitan area and make use of a banded population of approximately 100 breeding pairs of owls, two-thirds of which appear to be year-round residents. The study includes both descriptive and experimental components. The proportions of overwintering and migrating return breeders will be accurately determined through year-round weekly nest monitoring, including the use of an infrared video probe for underground observation of owls in their burrows. I also will attempt to verify these proportions through stable isotope analysis of adult feathers. Pending identification of winter molt feather tracts, I will compare adult isotopic signatures with an isotopic base map derived from feathers collected from locally reared juveniles. Proximate factors influencing the probability of overwintering will be assessed through manipulative and correlative means. The effect of food availability will be addressed through experimental supplementation with rodents, a preferred food of burrowing owls, during late summer and early fall. The effect of burrow availability will be assessed through use of the infrared probe to determine burrow integrity and by counting the number of satellite burrows associated with each nest burrow. I also will assess the relationship between reproductive success and overwintering by comparing nesting success and number of juveniles fledged by resident and migrant owls.